The invention relates to a novel tumor-associated antigen (TAA), derivatives and fragments thereof, antibodies thereto, and nucleic acids encoding the TAA and its derivatives and fragments. The invention further relates to the use of such molecules in the diagnosis and treatment or prevention of tumor diseases.
The immune system has the task of protecting the body from a number of different microorganisms and actively fighting these microorganisms. The importance of an intact immune system is apparent particularly in the case of inherited or acquired immunodeficiencies. The use of prophylactic vaccine programmes proved in many cases to be an extremely effective and successful immunological intervention in the fight against viral or bacterial infectious diseases. It has also been found that the immune system is also involved to a large extent in eliminating tumour cells. Recognition of the tumour associated antigens (TAAs) by components of the immune system plays a crucial role. In the broadest sense, any (peptidic or non-peptidic) component of a tumour cell which is recognised by an element of the immune system and leads to stimulation of an immune response can act as an immunogenic tumour antigen. Those tumour antigens which not only evoke an immunological reaction but also cause rejection of the tumour are of particular importance. The identification of specific antigens which are able to provoke an immunological reaction of this kind constitutes a major step in developing a molecularly defined tumour vaccine. Although it is not yet clear which elements of the immune system are responsible for rejection of the tumour, there is nevertheless consensus that CD8-expressing cytotoxic T-lymphocytes (CTLs) play a major part (Coulie, 1997, Mol. Med. Today 3: 261-268). Particularly in those types of tumour (such as melanoma and kidney carcinoma) which have a relatively high spontaneous remission rate, a correlation has been found between the clinical progress and the increased appearance of CD8+- and CD4+-T-cells (Schendel et al., 1993, J. Immunol. 151: 4209-4220; Mackensen et al., 1993, Cancer Res. 53: 3569-3573; Halliday et al., 1995, World J. Surg. 19: 352-358; Kawakami et al., 1995, J. Immunol. 154: 3961-3968; Kawakami et al., 1996, Med. 45: 100-108; Wang, 1997, Mol. Med. 3: 716-731; Celluzzi and Falo, 1998, J. Immunol. 160: 3081-3085). Specific CTL clones were obtained either from tumour-infiltrating lymphocytes (TIL) or peripheral mononuclear blood cells (PBMC) after co-cultivation with generally autologous tumour cells and cytokine stimulation in vitro. Both in animal models and in human cell culture systems cultivated in vitro, the T-cell response against tumour cells was increased by transfection of tumour cells with cytokines (van Elsas et al., 1997, J. Immunother. 20: 343-353; Gansbacher et al., 1990, J. Exp. Med. 172: 1217-1224; Tepper et al., 1989, Cell 57: 503-512; Fearon et al., 1990, Cell 60: 397-403; Dranoff et al., 1993, Proc. Natl. Acad. Sci. U.S.A 90: 3539-3543).
In the light of the correlation between remission and the involvement of CD8+-T cells, the identification of tumour associated antigens (TAA) which are recognised by CD8-positive CTLs is a specific prime objective towards developing a tumour vaccine (Pardoll, 1998, Nature Medcine 4: 525-531; Robbins and Kawakami, 1996, Curr. Opin. Immunol. 5: 658-63). Whether other cell types of the immune system such as for example CD4+-T-helper cells play an important part is not yet clear; a number of studies with MAGE-3/HLA-A1 peptides in melanoma patients indicated this (Marchand et al., 1995, Int. J. Cancer 63: 883-885; Boon et al., 1998, Cancer Vaccine Weekxe2x80x94International Symposium, New York, October 1998; abstract S01). In recent years a number of TAAs which are recognised by CTLs have been identified (Boon et al., 1994, Annu. Rev. Immunol. 12: 337-365; van den Eynde and van der Bruggen, 1997, Curr. Opin. Immunol. 9: 684-693).
T-cells recognise antigens as peptide fragments which are presented on the cell surfaces of MHC molecules (major histocompatibility complex, in man xe2x80x9cHLAxe2x80x9d=xe2x80x9chuman leukocyte antigenxe2x80x9d). There are two types of MHC molecules: MHC-I molecules occur in most cells with a nucleus and present peptides (usually 8-10-mers) which are produced by proteolytic degradation of endogenous proteins (so-called antigen processing). Peptide: MHC-I complexes are recognised by CD8-positive CTLs. MHC-II molecules occur only on so-called xe2x80x9cprofessional antigen-presenting cellsxe2x80x9d (APC) and present peptides of exogenous proteins which are absorbed and processed in the course of endocytosis by APC. Peptide: MHC-II complexes are recognised by CD4-helper-T cells. By interaction between the T-cell receptor and peptide:MHC complex, various effector mechanisms may be triggered which lead to apoptosis of the target cell in the case of CTLs. This occurs if either the MHC (e.g. in the case of transplant rejection) or the peptide (e.g. in the case of intracellular pathogens) is recognised as foreign. In any case, not all the presented peptides meet the structural and functional requirements for effective interaction with T-cells (as described by Rammensee et al., 1995, Immunogenetics 41: 178-228 and hereinafter).
In principle, a number of methods of administration are possible for using TAAs in a tumour vaccine: the antigen can either be administered as a recombinant protein with suitable adjuvants or carrier systems or it may be given as cDNA coding for the antigen in plasmid (DNA vaccine; Tighe et al., 1998, Immunol. Today 19: 89-97) or viral vectors (Restifo, 1997). Another possibility is to use recombinant bacteria (e.g. listeria, salmonella) which recombinantly express the human antigen and have an adjuvant effect as a result of their additional components (Paterson, 1996, Curr. Opin. Immunol. 5: 664-669; Pardoll, 1998, Nature Medcine 4: 525-531). In all these cases, the antigen has to be processed and presented by so-called xe2x80x9cprofessional antigen presenting cellsxe2x80x9d (APC). Another possibility is to use synthetic peptides (Melief et al., 1996, Curr. Opin. Immunol. 8: 651-657) which correspond to the equivalent T-cell epitopes of the antigen and are either loaded onto the APC from outside (Buschle et al., 1997, Proc. Natl. Acad. Sci. U.S.A. 94: 3256-3261; Schmidt et al., 1997, Proc. Natl. Acad. Sci. U.S.A 94: 3262-3267) or absorbed by the APC and transferred intracellularly to the MHC I molecules. The most therapeutically efficient method of administration of a specified antigen is generally determined by clinical trials.
The antigens or epitopes thereof recognised by the tumour-specific CTLs include molecules which can come from any protein classes (e.g. transcription factors, receptors, enzymes; for a survey see Rammensee et al., 1995, Immunogenetics 41: 178-228; Robbins and Kawakami, 1996, Curr. Opin. Immunol. 8: 628-636). These proteins do not necessarily have to be located on the cell surface, as is necessary for recognition by antibodies. In order to act as a tumour specific antigen for recognition by CTLs or in order to be used for therapy, the proteins must meet certain conditions: first of all, the antigen should be expressed exclusively by tumour cells or should occur in so-called xe2x80x9ccriticalxe2x80x9d normal tissues not at all or only in smaller concentrations than in tumours. Critical normal tissues are essential tissues; an immune reaction directed against them would have severe, in some cases lethal consequences. Secondly, the antigen should be present not only in the primary tumour but also in the metastases. Furthermore, with a view to broad clinical use of the antigen, it is desirable for it to be present in high concentrations in several types of tumour. One further precondition for the suitability of a TAA as an effective ingredient of a vaccine is the presence of T-cell epitopes in the amino acid sequence of the antigen; peptides derived from the TAA should lead to an in vitro/in vivo T-cell response (xe2x80x9cimmunogenicxe2x80x9d peptide). Another criterion for selecting a clinically broadly applicable immunogenic peptide is the frequency with which the antigen is encountered in a given population of patients.
The immunogenic tumour-associated antigens (TAAs), which have already largely been shown to have T-cell epitopes, can be divided into a number of categories, including viral proteins, mutated proteins, overexpressed proteins, fusion proteins formed by chromosomal translocation, differentiation antigens, oncofoetal antigens (Van den Eynde and Brichard, 1995, Curr. Opin. Immunol. 7: 674-681; van den Eynde and van der Bruggen, 1997, Curr. Opin. Immunol. 9: 684-693).
The methods of identifying and characterising TAAs which form the starting point for the development of a tumour vaccine are based on the one hand on the use of CTLs which have already been induced in patients (cellular immune response) or antibodies (humoral immune response), or are based on drawing up differential transcription profiles between tumours and normal tissues. In the former case, the immunological approach, patient CTLs are used for screening eukaryotic tumour-cDNA expression libraries which present the CTL-epitopes via MHC-I molecules (Boon et al., 1994, Annu. Rev. Immunol. 12: 337-365), whereas by using high affinity patient antisera prokaryotic cDNA expression libraries, the presence of TAAs can be searched directly via immunoblot analysis of the individual plaques (Sahin et al., 1995, Proc. Natl. Acad. Sci. U.S.A. 92: 11810-11813). A combination of CTL reactivity and protein-chemical processes produces the isolation of peptides isolated from MHC-I from tumour cells, which are preselected by reactivity with patient CTLs. The peptides are washed out of the MHC-I complex and identified by mass spectrometry (Falk et al., 1991, Nature 351: 290-296; Woelfel et al., 1994, Int. J. Cancer 57: 413-418; Cox et al., 1994, Science 264: 716-719). The approaches which use CTLs to characterise antigens involve substantial costs or are not always successful, owing to the need to cultivate and activate CTLs. Methods of identifying TAAs which are based on comparing the transcription profile of normal and tumour tissue are many and varied; these include differential hybridization, the establishing of subtraction cDNA banks (xe2x80x9crepresentational difference analysisxe2x80x9d; Hubank and Schatz, 1994, Nucleic Acids Res. 22: 5640-5648; Diatchenko et al., 1996, Proc. Natl. Acad. Sci. U.S.A. 93: 6025-6030) and the use of DNA chip technology or the SAGE method (Velculescu et al., 1995, Science 270: 484-487). In contrast to the above-mentioned immunological method using patient CTLs, when using molecular biological methods it is necessary to show that the potential antigen candidates discovered by this method are tumour-specific (tumour-associated) and do indeed have T-cell epitopes capable of triggering a cytotoxic T-cell response. In at least one case (NY-ESO/LAGE-1) an antigen was identified both by the use of patient sera and by RDA (Chen et al., 1997, Proc. Natl. Acad. Sci. U.S.A. 94: 1914-1918; Lethe et al., 1998, Int. J. Cancer 76: 903-908), and moreover CTL-epitopes of this antigen and a simultaneous spontaneous humoral and T-cell response were described in one patient (Jager et al., 1998, J. Exp. Med. 187: 265-270).
The present invention relates to a new tumor-associated antigen designated R11. The invention further relates to R11 fragments and derivatives, nucleic acids encoding R11 and R11 fragments and derivatives, and antibodies and antibody fragments thereto which display one or more functional activities of the R11 protein such as specifically binding the R11 protein, inducing or augmenting an immune response (e.g., induction of CTLs, induction of antibodies), or treating or preventing cancer (e.g., reducing the volume or inhibiting the growth of a tumor that expresses R11).